The Generation of Somatic and Heritable Variation in Response to Stress

In many organisms, including all higher plants, the life cycle is such that somatic mutations have the potential to be inherited. The rate at which somatic mutations arise in higher plants can be affected by a number of factors, including the environment in which the plants grow. One well-documented case in which this occurs is the environmental induction of heritable changes in flax. In this system, phenotypic and genomic changes can arise as a consequence of the particular environment under which plants are allowed to develop. These changes, which occur in a single generation, can be stably inherited for a large number of generations. The majority of the genomic alterations occur in the highly repeated sequences, although not all the sequence families alter to the same extent. Even within a family there appear to be specific subsets that are especially labile, although the characteristics differentiating the labile subset from the rest of the family of similar (or identical) sequences is not known. Genomic changes have also been demonstrated when flax cells have been taken through a cycle of tissue culture and regeneration. In this case, the genomic changes were similar to those previously observed in response to particular environments. A possible role for these types of changes is the generation of bursts of variation in higher plants as a response to stress.